Allow me to be brief:

1. Yes, you will need to go through immigration. However, CAN has been experimenting with a system that works more like true TWOV: exit the plane, go through security and go back up to departures. I don't know if it's continuing now, but I would presume it is.
2. It helps if you speak Chinese.
3. While I haven't spent a lot of time in CAN, do be warned that there's a lack of shops and restaurants in the international area, and it could get pretty boring.

Hope this helps.